1. Field of the invention
The invention relates generally to the transport of spacecraft from the earth to the relatively low gravity environment above the earth and more particularly to the transport of spacecraft and fluid propellant.
2. Description of the Related Art
A fundamental objective in designing and building spacecraft is to minimize the overall mass of the spacecraft. This is in part because the mass of the spacecraft is a significant factor in determining what proportion of a spacecraft cargo carried aloft should comprise propellant for manuevering the spacecraft once it has entered the relatively low gravity environment above the earth and what proportion may comprise electronic, optical or other systems.
For a typical spacecraft powered by a motor using a fluid propellant, for example, the propellant may comprise approximately 75% of the combined weight of the spacecraft and the propellant. A fluid propellant powered spacecraft launched from the space shuttle for geosynchronous orbit about the earth ordinarily requires enough propellant to propel the spacecraft from a relatively low parking orbit about the earth to a generally elliptical transfer orbit, to propel the spacecraft from a transfer orbit to a substantially circular geosynchronous orbit and to perform stationkeeping manuevers during the operational lifetime of the spacecraft.
In earlier spacecraft launches, fluid propellant usually was carried aloft within containers supported by support structure integral to the spacecraft. During launch from earth to the relatively low gravity environment above the earth, the rapid acceleration and vibration of the fluid propellant often resulted in loading of the propellant with forces equal to many times the force that the earth's gravity would exert on the propellant if it were at rest on the surface of the earth. Consequently, containers containing the propellant and support structure supporting it had to be sturdy enough to withstand such high loading. Unfortunately, sturdier containers and support structure generally were more massive. Thus, the containers and support structure of earlier spacecraft had to be massive and sturdy enough the withstand the high loading of the propellant during the launch.
In the past, a spacecraft often was staged to reduce its overall mass after it entered the relatively low gravity environment above the earth. For example, spacecraft were built which, during the transfer orbit, staged the spacecraft motor which propelled the spacecraft from the parking orbit to the transfer orbit.
While earlier schemes for reducing spacecraft mass by staging expendable spacecraft components generally were successful, there were shortcomings with their use. For example, staging usually necessitated the incorporation into the spacecraft of relatively complex systems used to accomplish the staging, and these systems often added to the mass of the spacecraft. Furthermore, there was an inherent risk that the staging would be unsuccessful and would leave the spacecraft disabled. Finally, much of the sturdy support structure used to support the fluid propellant during launch often was not easily separable from the spacecraft and, therefore, could not be staged.
Thus, there has been a need for an apparatus and a method for transporting a spacecraft and fluid propellant for use therein from the earth to a relatively low gravity environment above the earth without the need to incorporate into the spacecraft a support structure sturdy enough to support the fluid propellant during the transport. The present invention meets this need.